JPS60154261A - Reversal developing method - Google Patents

Abstract

PURPOSE:To form a sharp image by performing reversal development while putting the gap between a developer conveyor which conveys plural-component developers and an image carrier which holds an electrostatic latent image, and the amplitude and frequency of the AC component of a development bias voltage in specific relation. CONSTITUTION:A photosensitive drum 9 is exposed with a recording signal from a data recording part to record an electrostatic latent image. The plural-component developer 31 is contained in the developer reservoir 38 of a developing device 11, and when the developer 31 conveyed onto a sleeve 11A while its thickness is controlled by a napping controlling blade 30 reaches a development area 39, the electrostatic latent image recorded on the drum 9 is developed on reversal basis through the operation of the potential of the drum 9 and electric field by an AC power source 37 and a DC power source 36. Then, an expression is satisfied, where VAC(V) is the amplitude of the voltage of the power source 37, f(Hz) is the frequency, and d(mm.) is the gap between the drum 9 and sleeve 11A. Thus, a sharp image is formed without density deficiency nor fogging.

Description

[Detailed description of the invention] 1. Industrial application field The present invention relates to a reversal development method.

2. Prior Art First, an outline of an electrophotographic copying machine as a recording device using a conventional image carrier will be described. A document placed on a movable document table is irradiated by an exposure lamp, and this reflected light passes through a reflective mirror, lens, etc. to an image carrier (for example, a photoreceptor drum) whose surface is already charged by a charging electrode. be guided. The photoconductor drum is configured to rotate in synchronization with the movement of the document table, and when the light reflected from the document is sequentially exposed to the photoconductor drum, the potential decreases in accordance with the amount of II light, so the surface of the photoconductor drum is An electrostatic latent image is formed.

The potential of the portion where the amount of exposure from the original is small is relatively high.

When such an electrostatic latent image is developed using, for example, a magnetic brush development method, toner charged to the opposite polarity to that of the photoreceptor drum adheres to the unexposed areas, and the surface of the photoreceptor drum is left with a toner charged to a polarity opposite to that of the photoreceptor drum. A toner image is formed.

This toner image is transferred by the transfer pole onto the copy paper fed from the paper feeder. The copy paper onto which the toner image has been transferred is separated from the photoreceptor drum by a separation electrode, and after the toner image is fixed on the copy paper by a fixing device, it is sent to a paper discharge tray. Meanwhile, the photosensitive drum continues to rotate during this time, and after residual charges are removed by a static eliminator, excess toner on the surface of the photosensitive drum is removed by a cleaning device, and the photosensitive drum is subjected to the next copying process. In this copying machine, since the image corresponding to the original is directly transferred onto copy paper, copying is performed using a regular developing method.

On the other hand, the recording device includes an OFT, a laser, and an LED that operate according to recording signals from the data recording section.

2. Description of the Related Art There is an apparatus that forms an electrostatic latent image on a photoreceptor drum using an LCD or the like as an exposure means, and develops and transfers the image to create a recorded image.

In a document consisting of characters, lines, etc., if you compare the area of the part recorded with ink or the like with the area of the unrecorded part, the area of the recorded part is usually much smaller. Therefore, when forming an electrostatic latent image on the photoreceptor drum using the exposure means as described above, it is better to expose only the recorded area with a small area using the reversal development method and have the toner adhere there. It is possible to lengthen the lifespan of the recording medium and to shorten the recording time. Further, the reversal development method must be used when a positive recording is directly obtained from a negative original in a copying machine.

As a conventional technique of the reversal development method, for example, Japanese Patent Application Laid-open No. 1986-
No. 89733, Japanese Patent Application Laid-Open No. 57-12836, etc., propose means for applying a DC voltage substantially the same as the latent image potential of the photoreceptor drum to the sleeve and superimposing an AC voltage thereon. However, when the present inventor performed reversal development using the above-mentioned means, there were almost no cases in which a clear record was obtained on the recording paper, and in many cases only an unclear recorded image was obtained due to lack of density or fog. Ta.

This is because the reversal development method requires the toner to adhere to the light-exposed portion of the photoreceptor drum that has a low latent image potential (small absolute value), which has an inherent problem that is different from the regular development method. Because there is. (In other words, in reversal development, it is necessary to apply a developing bias equal to the latent image potential of the exposed area to the developer carrier during development. However, due to environmental changes, changes over time, etc. The partial potential changes easily, causing fogging and density reduction.■ As the toner on the image carrier moves away from the developer conveying member, the adhesion force with the image carrier decreases.On the other hand, oscillating electric field lines, Due to the two effects of toner supply and toner withdrawal, toner images tend to be disturbed. On the other hand, as a developer used in the above-mentioned recording device,
There are two-component developers consisting of toner and carrier, and one-component developers consisting only of toner. Two-component developers are relatively easy to control triboelectric charging of toner particles, prevent agglomeration of toner particles, have good magnetic brush bristles, have excellent abrasion properties on the image bearing surface, and are easy to clean. Since it has the advantage of exhibiting a sufficient leaning effect even when used in combination, it is widely used even though it is necessary to control the amount of toner particles relative to carrier particles.

It should be noted that this two-component developer has conventionally generally used one in which the average particle size of the magnetic toner particles is several tens to several hundred μm and the average particle size of the non-magnetic toner particles is several tens of μm. However, such a developer has a problem in that it is difficult to obtain a high-quality image that reproduces delicate lines, dots, or differences in shading because the toner particles and even carrier particles are coarse. Therefore, in order to obtain high-quality images, conventional methods have been used, such as coating carrier particles with resin, improving the magnet inside the sleeve, and examining the bias voltage applied to the sleeve.
Although many efforts have been made, the reality is that stable and fully satisfactory images still cannot be obtained. Therefore, in order to obtain high-quality images, it is considered necessary to make toner particles and carrier particles finer. However, the average particle size of toner particles is 20 μm.
Hereinafter, especially if the toner particles are made into fine particles of 10 .mu.m or less, (1) the influence of Fnanderwaals force appears on the Coulomb force during development, resulting in so-called fogging in which toner particles adhere to the ground portion of the image background. ■It becomes difficult to control triboelectrification of toner particles, making aggregation more likely. Further, as the carrier particles are made finer, (2) the carrier particles also come to adhere to the electrostatic image area of the image carrier. The reason for this is considered to be that the force of the magnetic bias is reduced and the carrier particles adhere to the image bearing member together with the toner particles.

The problem with micronization is that the side effects mentioned above are more noticeable and clear images cannot be obtained, so it is difficult to actually use micronization of toner particles and carrier particles. Met.

When such a finely divided two-component developer is used in the conventional reversal development method described above, only fogging and insufficient density can be recorded.

3. Purpose of the Invention The present invention was made to solve the above problems, and its purpose is to prevent insufficient density and fog even when using finely divided toner and carrier. To provide a reversal developing method capable of performing clear recording.

4. Structure of the Invention In other words, the present invention provides a structure in which a DC component and an AC component are connected between a developer transporting member that transports a developer composed of a plurality of components to a developing area and an image carrier holding an electrostatic latent image. In a reversal development method in which a toner image is formed on the image carrier by applying a developing bias voltage, the amplitude of the alternating current component of the developing bias voltage is Q (V), and the frequency is ((Hz
), the gap between the developer transporter and the image carrier is d
The present invention relates to a reversal developing method characterized in that, when (n+m), the following is satisfied: 1^c/<d-4>≧0.2.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a schematic cross-sectional view of a recording apparatus, in which a photosensitive drum 9 as an image carrier uniformly charged by a charging electrode 10 is
Only the recorded portion is exposed by the exposure means 7 operated by the recording signal from the data recording section 6, and the latent image potential of this portion is lowered. Photosensitivity, 9, □□2, 6, 1
．． Step 5.1 □, (('I J Toner of the same polarity as the charge polarity of the photoreceptor drum 9 is supplied by the sleeve IIA as a developer transporting member, and it adheres to the area where the latent image potential is low, so that the toner of the photoreceptor drum A toner image is formed on the separation pole 13. This toner image is transferred by the transfer pole 12 onto the recording paper 18 fed from the paper feed box 15 via the rollers 18 and 17. It is separated from the photoreceptor drum 9 by the conveyor belt 26 and sent to the fixing device 19.The fixing device 19 includes a heating roller 23 having a heater 22 inside, and a pressure roller 2.
4, and by passing the recording paper 18 between them, the toner image is fixed on the recording paper 18 and sent to the paper discharge tray 25. Meanwhile, the photosensitive drum 9 continues to rotate during this time, and after the residual charge is removed by the static eliminator 8, excess toner on the surface is removed by the cleaning device 14, and the photosensitive drum 9 is used for the next recording process.

FIG. 2 is an enlarged sectional view of the developing device 11 used in the recording apparatus of FIG. 1. In the developer reservoir 38, there is a developer 31 composed of carrier and toner, and as the stirring screw 32 rotates, the toner (8) is sufficiently charged by friction with the carrier. here,
When the sleeve IIA and/or the magnetic roll 34 rotate, the developer 31 is conveyed on the circumferential surface of the sleeve IIA. In FIG. 2, it can be seen that the magnetic roll 34 rotates in the direction of arrow A and the sleeve IIA rotates in the direction of arrow B, so that the developer 31 is conveyed in the direction of arrow B on the circumferential surface of sleeve IIA. It shows. The thickness of the developer 31 is regulated by the spike control blade 30, and the developer 31 forms a certain layer in the direction of the photoreceptor drum 9. When the developer 31 reaches the development area 39, the toner 28 is exposed on the photoreceptor drum 9 by the action of the electric field created by the latent image potential of the photoreceptor drum 9 and the AC and DC voltages applied as development bias voltages. adheres to the affected area. 37 is an AC power supply, 36 is a DC power supply, and R is a protection resistor. When the toner 28 is insufficient in the developer reservoir 38, the toner 28 is replenished from the toner hoch 27 by rotating the replenishment roller 29.

Hereinafter, an experiment conducted by the present inventor using this developing device 11 will be explained.

As explained in the prior art section, Japanese Patent Application Laid-Open No. 54-8973
With the method shown in Publication No. 3, etc., clear records cannot be written on the recording paper 18. Therefore, the present inventor has determined the gap d between the photosensitive drum 9 and the sleeve IIA (hereinafter simply referred to as gap d), the developer layer thickness, the AC voltage applied as the development bias voltage and its frequency, the DC voltage,
After conducting experiments with various changes in the amount of charge of the toner, etc., it was found that the amplitude (Oto peak) of the AC voltage, its frequency, and the gap d are closely related to the ability to write clear records on the recording paper 18. I found out.

FIGS. 3 and 4 are diagrams showing the results obtained from this experiment.

A photosensitive drum 9 having a photosensitive layer made of selenium is used as an image carrier, has a diameter of 120 (mm), and has a peripheral speed of 1
Rotates clockwise at 20 (mR1/s). A cylinder made of a conductive non-magnetic material (non-magnetic stainless steel, aluminum, etc.) with a diameter of 30 mm is used as the sleeve IIA, and rotates counterclockwise at a circumferential speed of 120 mm/s. The number of magnetic poles of the magnetic roll 34 is 6, the maximum magnetic flux density is 900 Gauss, and the rotation speed is 1000 (rpm).
to rotate clockwise. The spike control blade 30 is made of a magnetic material, and the gap with the sleeve IIA is 0.4 (mm), and the thickness of the developer layer is measured to be 0.5 (mm).
Met. In addition, as a developer, an average particle size of 30 (μm),
A magnetic carrier with a specific resistance of 16δG and an average particle size of 12 (μm)
), non-magnetic toner with a specific resistance of 1d+Ω■ in a weight ratio of 4=1
A mixture of these ratios was used.

In the developing device 11 configured as described above, the gap d (mm
), the alternating current bias voltage ■^c (V), this frequency f (Hz), etc. were varied, and the relationship between these parameters and image density was investigated.

Figure 3 shows the frequency factor of the AC component of the developing bias as 1 (K
Hz).

Curve A represents the latent image potential (Vs
max) is 600 (V), and the latent image potential of the exposed area (Vsmi
n) to 0 (V), DC bias voltage VDC to 500
(V), gap d is 0.5 (mm),) toner charge amount is 30 (μC/g), and when developing under the conditions that the developer layer and photoreceptor drum 9 are in contact, the AC electric field It shows the image density obtained when the amplitude EAC of the electric field was changed from 0'' (11) to 1.5 (K V , /no+).
The amplitude EAC of d is the value obtained by dividing the amplitude (V) of the AC voltage applied as a developing bias by the gap d (+u+). Curve B has V5max of 500 (V), V
oc is 450 (V), d is 0.3 (IIIll), toner charge amount is 15 (μC/g), photosensitive drum 9 and developer layer are in contact, and curve C shows Vbtaax as 600 (V).
), ' Vl) c is 500 (V), d is 0.7 (
n+m), the charge amount of the toner was 30 (μC/g), the developer layer and the photosensitive drum 9 were not in contact, and the curve was Vsaa.
x is 600 (V), VoC is 450 (V), d
1.0C+++n+),)ner charge amount to 20(μC
/g), the amplitude EAC of the alternating current electric field W is set to 0 to 1.5 (Kv/g) under the condition that the developer layer and the photoreceptor drum 9 are not in contact with each other.
l1lI11) Shows the image density obtained when changing the gusset.

As is clear from the curves in FIG. 3, the effect of the AC component appears when the amplitude EAC of the AC electric field is 200 (V/mm) or more.

In FIG. 4, the frequency f of the AC component applied as a developing bias is 2.5 (KHz).

(12) Curves B, C, and D are A at the time of the experiment in Figure 3.

It shows the image density obtained when the amplitude EAc of the alternating current electric field was varied from 0 to 3 (Kv/III) under the same conditions as those in B, C, and D. As shown in Figure 4, the amplitude EAC of the AC electric field is 500 (V/+n+n)
This is where the effect of the alternating current component appears. Note that when the DC component became approximately equal to the latent image potential of the non-image area, a high-density, fog-free image was obtained.

When a similar experiment was conducted under different conditions, the amplitude EAC and frequency factor of the alternating current electric field could be sorted out, and the results were as shown in Figure 5. In Fig. 5, ■ is an area where development unevenness is likely to occur, ■ is an area where the effect of the alternating current component of the developing bias does not appear, ■ is an area where breakdown is likely to occur, ■
and ■ indicate areas where the effect of the alternating current component of the developing bias appears, and ■ indicates a particularly preferable area. As is clear from FIGS. 3 and 4, when the amplitude EAC of the alternating current electric field is gradually increased from O, there is a region where the image density increases in proportion to the increase in EAC (for example, the curve in FIG. 3). In terms of C, the range is from 0.2 to 1.2 (KV/n+m)), and the range where the image density remains constant even if the EAC is increased (in the above example, 1.2 (KV/mn+) or more). It has become clear that there is a region of This is considered to be due to the following reasons.

In a region where the image density increases as the amplitude EAC of the alternating current electric field increases, toner with a small charge that did not detach from the sleeve 11A when the EAc was low begins to detach from the sleeve IIA as the EAc increases. , Therefore, EAc and image density are proportional.

In addition, in the area where the image density does not increase even if the amplitude EAC of the AC electric field is increased and the image density remains almost constant, it is assumed that the toner is already sufficiently vibrated by F and AC and the development is approaching saturation. It will be done.

Furthermore, the higher the frequency of the AC component of the developing bias, the lower the image density, which is thought to be related to the ability of the toner to follow the amplitude of the AC electric field. In other words, when the frequency becomes high, the toner cannot follow it and vibrate,
It is assumed that the amplitude becomes substantially smaller and the image density decreases.

Based on the above experimental results, the inventor determined that the amplitude of the AC component of the developing bias is vAC(v), and this frequency is +(11
z), the gap between the photosensitive drum 9 and the sleeve "IIA" is d
When (nun), go to (2) We conclude that if reversal development is performed under the conditions that satisfy 〇/(d-+)≧0.2, it is possible to obtain clear recorded images with appropriate density and no fog. I got it.

If the amplitude EAC of the alternating current electric field becomes too high, so-called breakdown occurs, the image density decreases, and this noise may appear on the image. In order to prevent this, in addition to the above conditions, if ((VAc/d3-1000)min≦1.5 is satisfied, the failure due to breakdown can be removed.Furthermore, if sufficient images are In order to obtain the concentration, it is desirable to satisfy the condition of VAc/(d-(-)≧0.8).

In addition, in order to prevent uneven development due to AC components, ((
15) This frequency is 200 (Hz) or more, and if a rotating magnetic roll 34 is used as a means for supplying the developer,
In this case, in order to prevent uneven development and images due to alternating current components and beats, it is preferable to set the frequency to 500 (Hz) or higher, and the alternating current components are superimposed on the direct current components.

The purpose of this is as follows: (1) To prevent toner from adhering to the non-image area (portion not exposed to n-light) of the photoreceptor drum 9.

(2) Breaking down the agglomeration of toner particles and facilitating separation of carrier and toner makes development easier.

(3) Prevent carrier scattering and adhesion to photoreceptor drum 9.

This will be explained in detail below.

As described in the prior art section, it is effective to make toner or carrier into fine particles in order to improve image quality. However, in general, when the average particle size of toner particles becomes smaller, the amount of charge (16) decreases qualitatively in proportion to the square of the particle size, and the adhesion force such as van der Waals force becomes relatively large. Once the toner particles become separated from the carrier particles, or once they adhere to the non-image area of the photoreceptor drum 9, they cannot be easily removed by rubbing with a conventional magnetic brush, resulting in fogging. In the conventional magnetic brush development method, such problems became noticeable when the average particle size of toner particles became 108 m or less.This reversal development method solves this problem by vibrating the development by the developer layer. This problem can be solved by carrying out the process under an electric field.In other words, the agglomeration of toner particles is destroyed by the electrically applied vibrations, and the toner particles are individually separated from the developer layer and applied to the image area of the photoreceptor drum 9. If the developer layer rubs against the photoreceptor drum 9 (contact development), the particles adhered to the non-image area of the photoreceptor drum 9. The toner particles can be easily removed or moved to the electrostatic image area, and the thickness of the developer layer can be adjusted between the photoreceptor drum 9 and the sleeve II.
When the gap with A is made thinner than d (non-contact development), toner particles with a low charge amount hardly migrate to the image area or non-image area, and are not rubbed against the photoreceptor drum 9. Therefore, toner particles do not adhere to the photoreceptor drum 9 due to frictional charging, and toner particles having a particle size of about 1 μm can now be used. Therefore, it is possible to obtain a clear toner image with good reproducibility in which the electrostatic latent image is faithfully developed.

Furthermore, since the oscillating electric field weakens the bond between toner particles and carrier particles, adhesion of carrier particles accompanying toner particles to photoreceptor drum 9 is also reduced. In particular, when the developer layer thickness is made thinner than the gap d between the photoreceptor drum 9 and the sleeve IIA, toner particles with a large amount of charge in the image area and non-image area vibrate under the oscillating electric field, and the strength of the electric field increases. In some cases, the carrier particles also vibrate, so that the toner is selectively transferred to the electrostatic image area of the photoreceptor drum 9, so that adhesion of the carrier to the photoreceptor drum 9 is significantly reduced.

Next, the carrier used in this reversal development method will be explained. It is desirable that the carrier has the following characteristics.

■Due to the small particle size, even if an electrostatic image is developed while being vibrated by an electric field, unevenness tends to appear in the toner image.■The toner concentration in the developer layer becomes low, so high-density development is not possible. , etc. problems occur.

In order to solve this problem (2), the average particle size of the carrier particles can be reduced, and as a result of experiments, the effect begins to appear when the average particle size is 50 μm or less, and when the average particle size is 30 μm or less, the problem (2) is practically eliminated. It was found that this does not occur. Also,
The problem (2) can also be solved by making the magnetic carrier finer particles, which increases the toner concentration in the developer layer and enables high-density development. Note that the average particle diameter is a weight average particle diameter, and was measured using an Omnicon Alpha (manufactured by Bausch & Lomb) and a Coulter Counter (manufactured by Coulter).

■Contains thermoplastic resin.

As mentioned above, if the carrier is made smaller, it becomes more likely that the carrier will scatter or adhere to the surface of the photoreceptor drum 9, but with conventional carrier particles made only of magnetic material, the carrier particles that have migrated onto the recording paper are Since the carrier particles themselves are not fixed on the recording paper, there is a problem that they easily fall off, and when the carrier particles remaining on the photoreceptor drum 9 are removed by a cleaning device, they may scratch the surface of the photoreceptor drum 9 made of a photoreceptor. The problem is that it is easy to attach. These problems are solved by using thermoplastic resin for the magnetic carrier particles. That is, by using a thermoplastic resin for the magnetic carrier particles, the carrier particles attached to the recording paper are also fixed by heat and pressure, and are also removed from the surface of the photoreceptor drum 9 by the cleaning device. This eliminates the possibility of damaging the surface of the photoreceptor drum 9.

Even if the carrier particles have an average particle size of 5 to 15 μm, the above (
The problem of carrier adhesion/scattering does not cause any practical trouble (20).

■ Spheroidizing carrier particles Spheroidizing carrier particles improves the agitation performance of toner and carrier and the transportability of developer, and also improves the charge controllability of toner, so that toner particles can be separated from each other and toner particles and carrier particles. Prevents aggregation from occurring.

Therefore, the problems of carrier adhesion and scattering are alleviated.

From the above, the magnetic carrier particles of the two-component developer used in this reversal development method are particles consisting of magnetic particles and resin, such as resin dispersion systems of magnetic powder and resin, or resin-coated magnetic particles, and more preferably Preferably, the particles are spherical and have an average particle diameter of preferably 50 μm or less, particularly preferably 3oIIm or less, and 5 μm or more.

Such magnetic carrier particles have iron as the magnetic material, similar to that in conventional magnetic carrier particles.

Metals such as chromium, nickel, and cobalt, or their compounds and alloys; ferromagnetic materials such as triiron tetroxide, γ-ferric oxide, chromium dioxide, manganese oxide, ferrite, and manganese-copper alloys; Or using paramagnetic particles, the surfaces of these particles are coated with resin such as styrene resin, vinyl resin, ethyl resin, rosin modified resin, acrylic resin, polyamide resin, epoxy resin, polyester resin, etc. Alternatively, it can be obtained by making particles from a resin containing fine magnetic particles dispersed therein, and then selecting the particle size of the obtained particles using a conventionally known average particle size selection means. In order to obtain spherical magnetic carrier particles, resin-coated carrier particles should be selected as spherical magnetic particles as possible and coated with resin, and magnetic particles should be coated with resin as much as possible. It is manufactured by applying a spheroidizing treatment using hot air or hot water after forming dispersed resin particles, or directly forming spherical dispersed resin particles by a spray drying method.

In addition to the above-mentioned effects, the magnetic carrier particles sphericalized by such a resin make the developer layer formed on the sleeve 11A uniform, and also make it possible to apply a high bias voltage to the sleeve IIA. It also has the effect of saying. That is, the fact that the carrier particles are spherical with resin is because (1) Generally, carrier particles tend to be magnetized and attracted in the long axis direction, but by sphericalization, this directionality is lost, and therefore, the developer layer is (2) Formed uniformly to prevent localized areas of low resistance and uneven layer thickness from occurring.
As the resistance of carrier particles increases, the edge portions seen in conventional carrier particles disappear, and the electric field no longer concentrates on the edge portions.As a result, even when a high bias voltage is applied to sleeve IIA, This provides the effect that discharging on the photosensitive drum 9 will not disturb the electrostatic latent image or cause breakdown of the bias voltage. The fact that this high bias voltage can be applied means that the effect of the developing bias having an AC component can be fully exhibited in this reversal developing method.
'zx・1 In relation to the fact that this high bias voltage can be applied (23), magnetic carrier particles made of resin have a resistivity of 10'Ω or more, especially 10'QcI11 or more. This resistivity is determined by placing the particles in a container with a cross-sectional area of 0.5M, tapping them, applying a load of 1 kg/cd on the packed particles, adjusting the amount of carrier to an appropriate amount, and When the carrier particles have a thickness of 1 ms + < 10 ms between the load and the bottom electrode.
This value is obtained by reading the current value when applying a voltage that generates an electric field of 00 V/c+a.If this resistivity is low, when a bias voltage is applied to sleeve IIA, there will be no charge on the carrier particles. is injected, making it easier for carrier particles to adhere to the photoreceptor drum 9 or for bias voltage breakdown to occur more easily.

From the above, magnetic carrier particles have a resin component, are spherical so that the ratio of the major axis to the minor axis is at least 3 times or less, have no protrusions such as needles or edges, and have low resistivity. 1
It is preferably fΩ or more, particularly 1d1Ω or more.

Next, as expected with the toner used in this reversal development method, the roughness of the image becomes noticeable. Usually 10 pieces/
For high-resolution development of fine lines lined up at a pitch of about m-,
There is no practical problem with toner having an average particle size of about 20 μm, but if you use micronized toner with an average particle size of 10 μm or less, the resolution will be significantly improved, and you will be able to produce sharp images that faithfully reproduce differences in shading. This will give you high-quality images. For the reasons mentioned above, the appropriate condition for the toner particle size is that the average particle size is 20 μm or less, preferably 10 μm or less. In addition, in order for the toner particles to follow the electric field, the average charge amount of the toner particles should be greater than 1 to 3 μC/g (preferably 3 to 30 μC/g).
0μC/g)□ is desirable. Particularly when the particle size is small, a high amount of charge is required.

Such toner can be obtained in the same manner as conventional toner. That is, it is possible to use a toner in which spherical or amorphous nonmagnetic or magnetic toner particles in conventional toners are sorted by an average particle size sorting means.

Among these, when the toner particles are magnetic particles containing fine magnetic particles, it is particularly preferable that the amount of the fine magnetic particles does not exceed 60-t%, especially 30 wt%. When the toner particles contain magnetic particles, the toner particles are influenced by the magnetic force of the magnet included in the sleeve IIA, which further improves the uniformity of the developer layer and reduces fogging. This prevents the occurrence of toner particles, and furthermore, scattering of toner particles becomes less likely to occur. However, if the amount of magnetic material contained is too large, the magnetic force between the carrier particles and the carrier particles becomes too large, making it impossible to obtain a sufficient developing density. As a result, frictional charging control becomes difficult, toner particles tend to be damaged, and toner particles tend to aggregate with carrier particles.

To summarize the above, the preferred toner in this reversal development method is to use the resin described above for the carrier and furthermore fine particles of magnetic material, and to which a coloring component such as carbon and a charge control agent, etc. are added as necessary. When produced by a method similar to a conventionally known method for producing toner particles, the particles have an average particle diameter of 20 μm or less, particularly preferably 10 μm or less.

In this reversal development method, a developer in which carrier particles and toner particles as described above are mixed in the same ratio as in a conventional two-component developer is preferably used.
If necessary, a fluidizing agent for improving the fluidity and sliding of the particles and a cleaning agent for cleaning the surface of the image bearing member are mixed therein. As a fluidizing agent, colloidal silica, silicon face, metal soap, or a nonionic surfactant can be used, and as a cleaning agent, a fatty acid metal salt, organic group-substituted silicon, or a surfactant such as fluorine can be used. I can do it.

The above are the conditions regarding the developer, and next, the conditions regarding the sleeve IIA which forms such a layer of developer to develop the electrostatic image on the photoreceptor drum 9 will be described.

7"J-7'111: [.../f-47'Xl! Pressure 1 application 6 gain 6 (developer transport carrier tll similar to that in the conventional developing method) is used, but in particular, the surface of the developer is A structure in which a break roll 34 having a plurality of magnetic poles is provided inside the sleeve IIA in which the ears are formed is preferably used.In such a sleeve IIA, the magnetic roll 3
By rotation of 4, te1. Since the developer layer formed on the surface of sleeve IIA moves on the surface in a wave-like manner, new developer is supplied one after another, and unevenness in the thickness of the developer layer is actually a problem. It won't be a problem. Then, the rotation of the magnetic roll β4 or the rotation of the sleeve II
The conveying speed of the developer layer due to the rotation of A is the same as that of the photosensitive drum 9.
It is preferable that the moving speed is almost the same as, or faster than. Further, it is preferable that the rotation of the magnetic roll 34 and the rotation of the sleeve IIA are carried in the same direction. Image reproducibility is better in the same direction than in the opposite direction. However, it is not limited to these.

The thickness of the developer layer formed on the sleeve IIA is preferably such that the adhered developer is sufficiently scraped off by the thick spike control blade 30 to form a uniform layer (28); The gap d between the sleeve IIA and the photosensitive drum 9 is preferably several tens to 2000 μm. If this gap becomes too narrow than several tens of micrometers, it becomes difficult to form a developer layer that acts uniformly, and it becomes impossible to supply sufficient toner particles to the developing section, making it impossible to perform stable development. 6. Also, the gap d is 200
When it exceeds 0 μm, the counter electrode effect decreases,
It becomes impossible to obtain a sufficient development density, and the edge effect that more toner adheres to the contours than the center of the electrostatic image increases. In this way, when the gap d becomes extreme,
On the other hand, it is difficult to make the thickness of the developer layer of sleeve IIA appropriate, but the gap d can be set to several tens of degrees. um~20
If the thickness is within the range of 0.00 μm, the thickness of the developer layer can be formed appropriately. Therefore, it is particularly preferable to set the gap d and the thickness of the developer layer to conditions such that the developer layer does not come into contact with the surface of the photoreceptor drum 9 but is as close to it as possible. This prevents scratches and fog from occurring due to rubbing of the developer layer during electrostatic image toner development.

5. EXAMPLE A specific example of a reversal developing method performed using the developing device 11 and developer 31 described above will be described with reference to FIG.

A photosensitive drum 9 having a large lh upper selenium photosensitive layer is used as an image carrier, has a diameter of 120 (++on), and rotates counterclockwise at a circumferential speed of 120 (mm/s). The number of magnetic poles of the magnetic roll 34 is 6, the magnetic flux density is 900 Gauss, and the rotation speed is 1000 (rpm).
to rotate clockwise. The spike control blade 30 is made of a magnetic material, and the gap with the sleeve IIA is 0.4 (mm), and the thickness of the developer layer is measured to be 0.5 (+nm).
Met. The gap d between the photosensitive drum 9 and the sleeve IIA was set to 0.8 (va), and the developer described below was used.

As the carrier particles, ferrite particles with an average particle size of 25 μm are suspended in hot air, and the same styrene/acrylic resin used for the toner particles is melted with a solvent and sprayed from a nozzle to adhere to the particles, and then dried. The average particle size obtained was 30 (μm), and the magnetization was 50 (
emu/g), resin-coated spherical carrier particles with a resistivity of 10100111 or more were used, and the toner particles were 100 parts by weight of styrene/acrylic resin (HIMER UP 110 manufactured by Sanyo Chemical Co., Ltd.) and carbon black (MA- 100) Using non-magnetic particles obtained by pulverizing and granulating particles with an average particle diameter of 10 μm, which are made of 10 parts by weight of nigrosine and 5 parts by weight of nigrosine, and spheroidized with hot air, a developer is produced using the apparatus shown in Fig. 2. Development was carried out under conditions such that the toner particle ratio of the developer 31 in the reservoir 38 was 10 wt % relative to the carrier particles. The average charge amount of the toner at this time was (15 μC/g).

The latent image potential of the photosensitive drum 9 is 600 (V) in the non-image area (unexposed area) and 0 (V) in the image area (exposed area).
v). On the other hand, development bias 1 performs non-contact reversal development under the following conditions: 500 (V) for the DC component and 500 (V) for the AC component, and then transfers it onto plain paper using a corona discharge transfer device. As a result of fixing through a heated roller fixing device with a surface temperature of 140°C, the resulting image on the recording paper was extremely clear with no edge effects or fog, and with high density. I obtained recording paper and was able to obtain a stable and unchanged image from beginning to end.

SuJ [vomit] The differences from Example 1 are as follows.

As carrier particles, the same styrene/acrylic resin as in Example 1 containing 50wt% of fine ferrite particles with an average particle size of 0.2 (μm) was pulverized and then treated with hot air.The average particle size was 20 (μm). , magnetization is 30 (81117g)
, using spherical particles with a resistivity of 10 Ω (2) or more, and having the same average particle size as in Example 1 as toner particles, 5 (μ
Using the spherical non-magnetic particles of m), development was carried out using the apparatus shown in FIG. 2 under conditions such that the toner particle ratio of the developer 31 in the developer reservoir 38 was 5 wt % relative to the carrier particles (32). . The average charge of the toner was 30 (μC/g).

In addition, the number of rotations of the magnetic roll 34 is 500 (rpm),
The magnetic flux density was set to 1200 Gauss, the amplitude of the AC component of the developing bias was set to 2 (KV), and the frequency was set to 2 (KHz).

□Non-contact reversal development was performed under the above conditions, the image was transferred to plain paper by corona discharge, and then fixed by a heat roller fixing device with a surface temperature of 140°C. It was extremely clear with no effects or fog, and had a high density.I subsequently produced 50,000 sheets of recording paper and was able to obtain a stable and unchanged image from beginning to end.

Soutane Mashu The differences from Example 2 are as follows.

The gap d was 0.3 (am), the gap between the spike control blade 30 and the sleeve IIA was 0.4 (am)' (the thickness of the formed developer layer was 0.5 mm), and the developing bias was AC. The amplitude of the component was set to 400 (V), and the m-wave number was set to 700 (Hz).

Contact reversal development was performed under the above conditions, and the resulting image was corona-transferred onto plain paper, and then passed through a heat roller fixing device with a surface temperature of 140°C to fix it. As a result, the resulting image on the recording paper was free of edge effects and fog. , and it was extremely clear with high density, and although we subsequently produced 50,000 sheets of recording paper, we were unable to obtain images that remained stable and unchanged from beginning to end.

In the above embodiments, only the amplitude and frequency of the AC component are specified, but the waveform may be a sine wave as shown in FIG. 6 or a rectangular wave as shown in FIG. Good too. Further, the waveform is not limited to these waveforms, and any waveform of alternating current component can be applied as long as it has periodicity.

Note that the present invention can be further modified based on its technical idea. In the above embodiments, a two-component developer consisting of a toner and a carrier was explained as the developer, but a developer having three or more types of components, such as a developer consisting of two types of toner and a carrier that are charged to different polarities, may also be used. good.

Further, the present invention can be applied not only to electrophotographic recording systems but also to non-impact printers such as electrostatic recording systems.

6. Effects of the Invention According to this reversal development method, a clear image can be formed on the image carrier by supplying the developer comprising a plurality of components to the image carrier.

That is, as shown in the present invention, when a toner image is reversely developed on an image carrier, the gap d (mIl) between the developer conveying member and the image carrier is
l), if the amplitude VAc (V) of the AC voltage applied between the developer conveying member and the image bearing member and this frequency ((Hz)) are set to satisfy vAC/(d・chi)≧0.2. Even now, it is possible to form a clear toner image on an image carrier without fogging or lack of density even with a finely divided developer.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 show the apparatus used to carry out the present invention. (dD) Figure 2 is a cross-sectional view of the developing device, Figures 3 and 4 are diagrams showing image density when the amplitude of the alternating current electric field is varied. ! Figure 5 is a characteristic diagram of image density when changing the amplitude and frequency of the AC electric field. Figures 6 and 7 are AC waveform diagrams! be. 2 Regarding the symbols used in the drawings, 7...
. . . Exposure means 9-1111 . . . Photosensitive drum, 11 . . . Developing device 11A . . . - Sleeve 18 . ---1--Toner 30--Stickling regulating blade 31--Developer 32--Stirring screw. 34--...-Magnetic roll d-----Gap between photosensitive drum and sleeve (36
). Agents: Patent Attorneys Aisaka, Hiroshi (and 1 other person) Kamibetsu Kikaia 4@! ″″′

Claims (1)

[Scope of Claims] 1. A developing bias having a DC component and an AC component between a developer transporting body that transports developer consisting of a plurality of components to a developing area and an image carrier holding an electrostatic latent image. In a reversal development method in which an electrostatic latent image held by the image carrier is reversely developed by applying a voltage, the amplitude of the alternating current component of the development bias voltage is vAc (v), the frequency Q (Hz),
The gap between the developer transporter and the image carrier is d (++
m) A reversal development method characterized by satisfying VAC/(d −4) ≧0.2. 2. The reversal developing method according to claim 1, wherein the thickness of the developer layer on the developer transport member is smaller than the gap d between the developer transport member and the image carrier.